1. Field of the Invention
This invention relates to Multimedia Broadcast/Multicast Service in Wideband Code Division Multiple Access (hereinafter referred to as WCDMA) mobile communication system, more specifically relates to a method for signaling bearer connection of Multimedia Broadcast/Multicast Service on Iu interface (the interface between Radio Access Network and Core Network).
2. Description of the Prior Art
Multimedia Broadcast and Multicast Service (hereinafter referred to as MBMS) is a new service under standardization by 3rd Generation Partnership Project (hereinafter referred to as 3GPP). MBMS service is an unidirectional point-to-multipoint (p-t-m) service, whose most remarkable characteristic is that it can make use of radio resources and network resources efficiently.
The architecture of the MBMS system is described in brief in combination with FIG. 1.
MBMS network structure adds new network elements based on the core network of General Packet Radio Service (hereinafter referred to as GPRS). Broadcast and Multicast Service center 101 (hereinafter referred to as BM-SC) is the service control center of MBMS system. Gateway GPRS Supporting Node 102 (hereinafter referred to as GGSN) and Service GPRS Supporting Node 103 (hereinafter referred to as SGSN) constitute the transmission network of MBMS service and provide route for data transfer. Home Location Register 106 (hereinafter referred to as HLR) saves the data related to user and can provide services such as user's authentication or the like. UMTS Terrestrial Radio Access Network 104 (hereinafter referred to as UTRAN) provides radio resources for MBMS service over the air-interface. Iu 107 indicates the interface between Radio Access Network and Core Network. User Equipment 105 (hereinafter referred to as UE) is the terminal device for receiving data. Radio resources used by MBMS service are not dedicated for one user, but are shared by all users using this service.
(1) Signaling Connection Mode of the Existing Iu Interface
In order to transfer message of layer 3 between UE and CN, the existing Radio Access Network Application Part (hereinafter referred to RANAP) establishes a signaling connection for each activated UE. RANAP supports two modes, i.e. connection-oriented and connectionless-oriented.
(2) Signaling Connection Establishment and Release of the Existing Iu Interface
When information of UE and CN needs to be exchanged between Radio Network Controller (hereinafter referred to as RNC) and CN and there is no signaling connection control part (hereinafter referred to as SCCP) for this UE on Iu interface, it is started to establish a new SCCP connection. The establishment of SCCP connection is as follows:
I) RNC Initiates the Establishment of SCCP Signaling Connection;
When RNC receives a non-MAC (Media Access Control) message from UE for the first time and there is no Iu connection for this UE, RNC initiates the procedure of SCCP connection establishment. RNC sends a SCCP Connection Request message to CN, which includes a RANAP message in its data field.
II) CN Initiates the Establishment of SCCP Signaling Connection
CN initiates the establishment of SCCP signaling connection when executing relocation. CN initiates the establishment of Iu connection through sending a SCCP Connection Request message to RNC, which includes a RANAP message in its data field (optional).
Situations listed above are only those for SCCP connection establishment having been decided at present. And other situation will be introduced in the future.
On the occasion of normal release, the release of SCCP connection is initiated by CN. When CN finds that a signaling connection isn't needed any more, the connection will be released and CN sends a SCCP RELEASED message.
On the occasion of abnormal; both CN and RNC can initiate a release procedure.
(3) The Existing Relocation Procedure of Serving Radio Network Subsystem
The SRNS relocation procedure is described by 3GPP specification TR 23.846 v1.2.0. FIG. 2 shows the corresponding signaling flow. The detailed description for each step in the flow is as follows.
201 Source RNC decides to execute SRNS relocation procedure;
202 Source RNC sends a Relocation Demand message to the old SGSN;
203 The old SGSN forwards the Relocation Demand message to the new SGSN;
204 The new SGSN sends a Relocation Request message to the target RNC and a radio access bearer (hereinafter referred to as RAB) is established between the target RNC and the new SGSN. After the resources needed by RAB including resources of the user plane are successfully allocated,: the target RNC sends a Relocation Request Confirmation message to the new SGSN.
205 The new SGSN forwards a Relocation Response message to the old SGSN.
206 The old SGSN sends a Relocation Command message to the source RNC.
207 The source RNC starts to copy data and sends them to the target RNC through network protocol (hereinafter referred to as IP layer).
208 The source RNC sends a Relocation delivery message to the target RNC. This procedure is used to transmit SRNS Context to the target RNC and the role of SRNS converts from the source RNC to the target RNC.
209 When the target RNC receives the trigger message for relocation execution, it sends a Relocation Detecting message to the new SGSN. After that the target RNC starts to play the role of Serving Radio Network Controller (hereinafter referred to as SRNC).
210 The UE exchanges mobility related information with the target RNC, such as the new SRNC Identifier, the representation of location area and uplink user data exchanging between UE and the target RNC, etc.
211 If the SRNS relocation is a relocation occurring between different SGSNs, the new SGSN sends a Update PDP Context Request message to the corresponding GGSN after it receives the Relocation Detecting message. GGSN updates Packet Data Protocol (hereinafter referred to as PDP) context and returns back a Update PDP Context Response message. The new SGSN examines respective MBMS services in NBMS Context of UE. IF a certain service is joined by the first UE in SGSN, a GPRS Tunnel Protocol (hereinafter referred to as GTP) tunnel between SGSN and GGSN is established and MBMS Context is created in GGSN.
212 The target SRNC initiates a Relocation completion procedure after receiving a UTRAN Mobility Information Confirmation message. The new SGSN sends a Relocation completion message to notify the old SGSN of the completion of SRNS relocation procedure.
213 Release the Iu connection between the source RNC and the source SGSN and the user resources.
214 If the new Route Area Indication (hereinafter referred to as RAI) is different from that of the old, UE initiates a route location update procedure.
C1, C2 and C3 execute Customized Applications for Mobile network Enhanced Logic (hereinafter referred to as CAMEL).
Existing RANAP uses a signaling connection for each activated UE. MBMS service is a new point-to-multipoint service, whose feature is to make use of radio resources and network resources more efficiently through sharing; On Iu interface, the user plane of MBMS services is shared. If each UE uses one signaling connection, it will not only increase the traffic of the information on Iu interface and the processes on the RNC and SGSN side, but also be unable to solve completely the problem due to user mobility. In order to solve of the problem of user mobility, messages on the existing Iu interface need to be modified as well. Thus, a method for Iu interface connection oriented to MBMS service shall be proposed, which can not only make reasonable use of network resources, reduce processes on RNC and SGSN side and modifications to the existing message, but also can solve the problem of user mobility.
The existing Relocation Demand message is connection-oriented. If an user does not have other services (e.g. voice) except for receiving MBMS service, the Iu connection dedicated to the user has not been established. How to send a relocation demand message or establish Iu connection dedicated for the UE is the problem to be solved.
Since the user plane of MBMS service on Iu interface is shared, while the user plain and control plane of other services are dedicated, SRNS relocation procedure needs to be modified in this new mode;
Besides the connection method proposed in this invention (shared signaling connection is used on Iu for the same kind of MBMS service, and at the same time, dedicated Iu connection is established for the case in which other services besides MBMS service are received and the mobility of the UE occurs), there is another proposal that only shared Iu connection exists on Iu interface for UEs receiving MBMS. With respect to both these cases in which shared Iu connection exists, the method for establishing and releasing MBMS shared connection hasn't been provided in the existing SCCP connection establish procedure, and the situation for establishing shared connection shall be added to the conditions for establishing SCCP connection. Since MBMS is a new-introduced service, when the shared connection used for MBMS service shall be released is a problem unsolved in present specification.